Variable resistor



Jan. 13, 1959 smEt 2,868,933

VARIABLE RESISTOR Filed Nov. 4, 1957 1P3! 34 INVENTOR. Hg, 1 E90 51 Surge/man BY U. L ra-74w United States Patent Ofiice 2,868,933 Patented Jan. 13, 1959 a It.

VARIABLE RESISTOR Fred E. Singelman, Palatine, Ill., 'assignor to Admiral Corporation, Chicago, 11]., a corporation of Delaware Application November 4, 1957, Serial No. 694,213

6 Claims. (Cl. 201-62) This invention relates to resistors and more particularly to resistors of the variable resistance type.

The use of variable resistors in all types of electronic equipment is well known in the art. They may include the volume control type where the slider and the re sistance are in series with the circuit or the so-called potentiometer type where the resistance is in series and the slider is used to take ofi a voltage from across a portion of the resistance. Usually they have comprised a circular resistance member which is usually a support having a deposit of carbon thereon and a slider or swinger which is in slidable engagement with the carbon. Either one end or both ends of the resistance and/ or the swinger may be connected into a circuit. The above devices frequently take up considerable room.

By the present invention I have provided a variable resistance which is very cheap to manufacture, requires a minimum of space and is very reliable in operation. Still other advantages of the invention and the invention itself will become more apparent from the following description of an embodiment thereof which is illustrated by the accompanying drawings.

In the drawings:

Fig. 1 is a view partly in elevation and partly in section of a resistor of my invention and its manner of mounting on a chassis;

Fig. 2 is a plan view thereof;

Fig. 3 is a similar view of a modification thereof;

Fig. 4 is a plan view of the resistor of Fig. 3, and

Fig. 5 is an elevational view of a modified form thereof.

Briefly the invention contemplates a resistor having a tubular body with a slider movable into the body and making contact therewith, connections being made to the slider and the body. More particularly the invention contemplates a conductive coating on the exterior of the body which enables the resistance to be varied more accurately.

Referring to the drawings, throughout which like parts are designated by like reference characters, as viewed in Fig. 1 I provide a body of tubular resistance material which may be carbon or other type of material having a resitsance which may vary throughout a wide range depending upon the use for which it is intended.

The interior of the body is cored at 11 to provide a longitudinally extending channel which may be of circular or polygonal cross-section.

One end of the body is received in a cap 15 of metal, the cap being provided with a flange 16 and which is designed to provide a press fit in a mounting hole in a chassis 17.

In this instance the cap serves as a connection to the end of the body as well as a mounting for the body in a chassis. The shape of the cap may take various forms of which there are many well known to those versed in the art. If desired it may be provided tongues 18 which engage with the chassis and help retain the cap in place in the chassis.

One end of the cap is provided with an internally threaded boss 20 adapted to receive a threaded body 21 of the slider which may be of metal. The end of the screw is provided with a screw driver slot 22 or its equivalent socket 22 as shown in Fig. 3 for engagement by a screw driver or by a wrench of the so-called Allen type. Obviously it could be provided with a hand manipulated knob if desired. It is apparent that the cap 15 could be soldered into a printed circuit board if desired.

The end of the screw extends into the bore 11 and is preferably provided with a contact end 24 which may take the form of a split ball, the periphery of which is in pressure sliding contact engagement with the wall of the bore 11. Obviously this contact end could take other forms, such as cylindrical, but I have found that a nearly ball shaped end provides a very good operation characteristic. If the ball has a slightly elongated section in contact with the carbon wall, there is a reduction in contact resistance and slightly less surface noise during movement. In either event the split contact provides sufficient resiliency to afford a good and long lasting contact with the wall.

At one end of the exterior of the body I have metallized the body with a coating which completely surrounds the body at 30 and gradually tapers as illustrated at 31, surrounding less and less of the body proceeding in a direction toward the end cap until at the point 32 it terminates, the remainder of the body being uncoated. This coating may be applied by spraying, electroplating or by hand dipping, the only requirement being that it be closely adherent and that it provide a good electrical contact with the resistance body 10.

The end of the body has a metallic end cap 34 in electrical contact with the end of the body and the metallic coating. This cap may have a co-axial lead 35 extend ing from its end or the lead may extend from the side of the body.

In operation it will be seen that with the slider in the position indicated, the resistance material is interposed between the contact and the conducting body 30. As the screw is threaded into the body, the contact end moves toward and eventually arrives at a position opposite to the part of the body having the metallic coating. Further inward movement of the slider brings the contact end opposite that part of the body having more coating until finally, toward the lower end it arrives at the part having the most coating. Thus as the inward movement of the slider is effected the resistance continuously decreases. Connections may be made at 35 to the conductor and to the cap 15.

In Fig. 3 I have shown another embodiment particularly adapted for the so-called potentiometer type of resistance. In this instance each end of the body is pro vided with a resistance 30, the center being left uncoated. The coating can take exactly the same form as shown in Fig. 1 or can be reversely curved if desired. The cap in this instance could be insulated by an insulating sleeve 40 from the body 10. The slider then would have the greatest resistance from the end taps 30, when in the position shown. If moved in either direction the resistance would decrease toward the end tap in the direction in which it was moved and increase toward the other end tap. This as indicated provides an operation similar to the conventional potentiometer.

It will be apparent that the shape of the conductive material may be varied in both embodiments to provide a resistance which can vary linearly or in any other manner, and that the screw threaded slider could be replaced by one that had no screw threads and was adjusted by merely pulling in or out, although screw threads are to be desired since they allow a more precise adjustment.

It will also be apparent that the metallic coating enables a much higher resistance material to be used in the body and thus provide a much more compact device as compared to the prior art. For instance, this resistance could be made in the form of elements the diameter of which could be one eighth inch or less and as short as one half inch.

In Fig. 5, I have illustrated an embodiment particularly adapted to have the conductive outer element 30a applied by .printed circuit techniques wherein the conductor may be applied by rolling item. In this resistance the lower end 30a of the conductor completely surrounds the body and is connected by a conductive neck 36b to the next portion 30c which is of shorter width. The

width of each successive portion is less than the preceding one until the end part 300 is relatively narrow.

Having thus described my invention I am aware that numerou and extensive departures may be made therefrom Without departing from the spirit of the invention as defined by the appended claims.

I claim:

1. A variable resistor comprising a body of resistance material having a bore therein, a slider supported at one end of the body and having a contact portion disposed in said bore with limited contact with the wall thereof, and a highly conductive coating on the other side of said resistance body which completely covers the body at one end and gradually decreases in coverage toward the other end.

2. A variable resistor comprising a tubular body of resistance material having a lengthwise cylindrical bore therein, support means for said body at the end thereof, a slider adjustably threaded in said support and having a contact portion for limited contact with said resistance body disposed in the bore, and a highly conductive coating on the exterior of the resistance body having greater coverage of the body at one end and lesser coverage at the other end.

3. A device as described in claim 2 wherein connections are provided to the slider and to the highly conductive coating.

4. A variable resistor comprising a body of resistance material having a lengthwise bore therein, a slider extending lengthwise into said bore and contacting said resistance body at said bore, said slider being adjustable lengthwise along the bore, and highly conductive material contacting the outside of said resistance body, the area of said conductive material on the outside of the resistance body varying lengthwise along said body.

5. A variable resistor comprising a body of resistance material having a lengthwise bore therein, a slider having an elongated portion shaped and dimensioned to extend lengthwise into said bore in spaced relation to the wall of the bore and a contact portion connected to said elongated portion and snugly received in said bore in engagement with a limited portion of the wall of the bore, said slider being adjustable to vary the position of said contact portion lengthwise along the bore, and a highly conductive coating on the outside of said resistance body, said coating presenting a surface engaging the outside of said resistance body which varies in area lengthwise along the resistance body.

6. The variable resistor of claim 5, wherein there is provided a support member engaging and supporting one end of said resistance body, said elongated portion of the slider being threadedly mounted in said support member for adjustment into and out of said bore in the resistance body.

References Cited in the file of this patent UNITED STATES PATENTS 1,539,266 Mountford May 26, 1925 2,687,463 Riley Aug. 24, 1954 2,707,811 Projector May 10, 1955 

